1. Field of the Invention
The present invention relates to a disk device for reading a signal from or writing a signal to a disk using, for example, magnetism. In particular, the present invention relates to a disk device having access to a disk in different writing modes.
2. Description of the Related Art
A disk device, into which a flexible magnetic disk is loaded as a medium, includes a rotational driver for rotating a disk, a magnetic head, and a head transfer unit for transferring the magnetic head along the disk. The disk device further includes a CPU, buffer memory, and a controller including a generator for generating data to be written and a decoder. Data to be written, which is supplied from a host computer, is initially stored in the buffer memory. Subsequently, the data is formatted by the generator and is written to the disk using the magnetic head. A signal read from the disk using the magnetic head is decoded by the decoder. The decoded signal is first stored in the buffer memory and then transferred to the host computer.
The magnetic disk used herein is a low-capacity type, such as a 1 MB or 2 MB disk.
Writing modes for a low-capacity disk device include a modified frequency modulation (MFM) mode and a frequency modulation (FM) mode. A disk device is specified for either of the writing modes.
The MFM mode is a writing mode mainly used for a low-capacity magnetic disk of 1 MB or 2 MB. The two writing modes differ in output units for outputting clock bits. In the MFM mode, the cycle of a bit cell is half of that of the FM mode. The writing density of the MFM mode is twice that of the FM mode.
The rotational driver of the disk device includes a motor for rotating the magnetic disk. The rotation rate of the motor is set to be, for example, 360 rotations/minute (rpm) or 300 rpm.
The above conventional disk device is specified for either the MFM mode or the FM mode. Compatible operations, such as writing of data by the MFM-mode disk device in the FM mode, are not feasible using the conventional disk device.
If a single disk device is to write data in both the MFM mode and the FM mode, a host computer is required to send a command to the disk device, prior to writing to the disk, permitting discrimination between the MFM mode and the FM mode. Based on the command, the controller of the disk device switches between the writing modes. Since the specification of an interface in general use cannot cope with the above command, a special interface is required to be formed.
An interface connecting a general disk device and a host computer is based on, for example, the AT attachment packet interface (ATAPI) or the small computer system interface (SCSI), so as to be shared with another disk device. Since the MFM mode and the FM mode do not exist in the above interfaces, it is necessary to build a special interface specified to generate and control a special command that designates the writing mode, i.e., the MFM mode or the FM mode.
Accordingly, it is an object of the present invention to provide a disk device for eliminating or reducing the above problems. The disk device of the present invention automatically switches between writing modes using a command based on a general interface specification without using a special command.
According to one aspect of the present invention, there is provided a disk device including a rotational driver for rotatably-driving a disk, a head for writing a signal to the disk, a head transfer unit for transferring the head along the surface of the disk, and a controller for causing the head to perform writing to the disk in different writing modes. The controller switches between the writing modes based on a command signal of a data transfer rate supplied from a host computer.
As described above, the command signal (command) of the data transfer rate may be used to enable the disk device to automatically switch between the writing modes for the disk. The command designating the transfer rate includes a general command that the host computer already possesses. It is unnecessary to provide the host computer with-a program for generating a special command for switching between the writing modes. A special interface specification is also unnecessary.
The controller may transfer information on the rotation rate of the disk driven by the rotational driver to the host computer. The host computer may compute a command signal value of the data transfer rate to be supplied for switching between the writing modes based on the information on the rotation rate. Then, the writing modes may be switched based on the computed command signal value of the transfer rate.
Even when a motor forming the rotational driver of the disk device rotates at a rotation rate other than a predetermined 300 rpm or 360 rpm, the transfer rate in accordance with the rotation rate may be computed and then notified to the disk device. When the disk device arbitrarily increases the rotation rate in order to, for example, improve the transfer speed, the disk device may be notified of the transfer rate in accordance with the rotation rate and therefore appropriately switches between the writing modes without making an erroneous determination.
For example, the different writing modes include an FM mode and an MFM mode.
The controller provided in the disk device is set to drive and control the overall disk device by operations in accordance with the FM mode and the MFM mode. Based on the command signal of the data transfer rate from the host computer, the controller switches to control in the FM writing operation or the MFM writing operation.
For example, if a disk device is capable of employing both a low-capacity medium accessible in the writing modes of the FM mode and the MFM mode and a high-capacity medium accessible in writing modes other than those of the low-capacity medium, the disk device may automatically switch between the FM mode and the MFM mode by designating the transfer rate.
The switching control of the writing modes is not limited to the switching between the FM mode and the MFM mode, and alternatively, it may be used for switching between other writing modes. The disk is not limited to a flexible magnetic disk, and alternatively, it may be an optical disk or a magneto-optical disk. Specifically, the present invention is applicable to general disk devices capable of writing in modes with different data transfer rates.